Progress in the brightness, lumen efficacy and affordability of solid state light sources, such as light emitting diodes (LEDs), enables new lighting applications that are no longer restricted to niche markets. LEDs offer several advantages over traditional light sources, such as long life time, low operating voltage, small form factor (giving design flexibility), almost pure spectral colors, fast modulation of lumen output, instant on, etc. For these and other reasons, LEDs are becoming more and more suited for making lamps for a variety of applications such as color variable luminaires, spotlights, architectural lighting, stage lighting, etc.
For example, it is increasingly popular to provide luminaires where the user can create various atmospheres according to his wishes. This has lead to development of dual function lamps that e.g. may provide white task light directed downwards, and colored atmosphere light directed upwards in a single lamp.
Previously known dual function lamps comprise two stacked sub-systems: at the bottom a side-emitting LED source with white LEDs and optics to send the light down; at the top a side-emitting LED source with colored LEDs and optics to send the light up. Such a dual function lamp is known from WO2008047278 by the same applicant disclosing a luminaire comprising an upper light guiding layer and a lower light guiding layer, wherein a colored side-emitting LED source is accommodated in a circular opening in the upper light guiding layer for emitting light into the upper light guiding layer, and a white side-emitting LED source is accommodated in a circular opening in the lower light guiding layer for emitting light into the lower light guiding layer. The light from the upper light guiding layer is outcoupled upwards to provide colored atmosphere light, while the light from the lower light guiding layer is outcoupled downwards to provide white task light.
However, this arrangement requires two LED sources arranged in separate locations, i.e. one LED source containing the white LEDs for arrangement in the lower light guiding layer, and one LED source containing the colored LEDs for arrangement in the upper light guiding layer. In order to provide a luminaire at reduced cost it would be desirable to be able to arrange the white LEDs and the colored LEDs together.